USGS

 

Water Quality and Possible Sources of Nitrate in the Cimarron Terrace Aquifer, Oklahoma, 2003

J.R. Masoner and S.L. Mashburn

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2004-5221

Prepared in cooperation with the Oklahoma Department of Environmental Quality

This report is also available as a pdf.


Abstract

Water from the Cimarron terrace aquifer in northwest Oklahoma commonly has nitrate concentrations that exceed the maximum contaminant level of 10 milligrams per liter of nitrite plus nitrate as nitrogen (referred to as nitrate) set by the U.S. Environmental Protection Agency for public drinking water supplies. Starting in July 2003, the U.S. Geological Survey, in cooperation with the Oklahoma Department of Environmental Quality, conducted a study in the Cimarron terrace aquifer to assess the water quality and possible sources of nitrate. A qualitative and quantitative approach based on multiple lines of evidence from chemical analysis of nitrate, nitrogen isotopes in nitrate, pesticides (indicative of cropland fertilizer application), and wastewater compounds (indicative of animal or human wastewater) were used to indicate possible sources of nitrate in the Cimarron terrace aquifer.

Nitrate was detected in 44 of 45 ground-water samples and had the greatest median concentration (8.03 milligrams per liter) of any nutrient analyzed. Nitrate concentrations ranged from <0.06 to 31.8 milligrams per liter. Seventeen samples had nitrate concentrations exceeding the maximum contaminant level of 10 milligrams per liter. Nitrate concentrations in agricultural areas were significantly greater than nitrate concentrations in grassland areas.

Pesticides were detected in 15 of 45 ground-water samples. Atrazine and deethylatrazine, a metabolite of atrazine, were detected most frequently. Deethylatrazine was detected in water samples from 9 wells and atrazine was detected in samples from 8 wells. Tebuthiuron was detected in water samples from 5 wells; metolachlor was detected in samples from 4 wells; prometon was detected in samples from 4 wells; and alachlor was detected in 1 well. None of the detected pesticide concentrations exceeded the maximum contaminant level or health advisory level set by the U.S. Environmental Protection Agency.

Wastewater compounds were detected in 28 of 45 groundwater samples. Of the 20 wastewater compounds detected, 11 compounds were from household chemicals, 3 compounds were hydrocarbons, 2 compounds were industrial chemicals, 2 compounds were pesticides, 1 compound was of animal source, and 1 compound was a detergent compound. The most frequently detected wastewater compound was phenol, which was detected in 23 wells. N,N-diethyl-meta-toluamide (DEET) was detected in water samples from 5 wells. Benzophenone, ethanol- 2-butoxy-phosphate, and tributylphosphate were detected in water samples from 3 wells.

Fertilizer was determined to be the possible source of nitrate in samples from 13 of 45 wells sampled, with 15N values ranging from 0.43 to 3.46 permil. The possible source of nitrate for samples from the greatest number of wells (22 wells) was from mixed sources of nitrate from fertilizer, septic or manure, or natural sources. Mixed nitrate sources had 15N values ranging from 0.25 to 9.83 permil. Septic or manure was determined as the possible source of nitrate in samples from 2 wells. Natural sources were determined to be the possible source of nitrate in samples from 7 wells, with 15N values ranging from 0.83 to 9.44 permil.

Contents

Abstract

Introduction

Purpose and Scope

Description of study area

Hydrogeology

Land use

Historical pesticide use

Acknowledgments

Methods

Selection of sampling sites

Ground-water sampling and analysis methods

Statistical analysis

Water quality in the Cimarron terrace aquifer

Water properties

Nutrients

Nitrogen isotopes

Pesticides

Wastewater compounds

Possible sources of nitrate

Summary

Selected references

Appendixes


This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.


Download the Report (PDF, 2.8 MB).


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For more information about water resources in Oklahoma is available on the World Wide Web at http://ok.water.usgs.gov.




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